Study On Current Characteristics And Wave-current Interaction In The Bohai Bay

Bohai Sea is the only semi-enclosed inland sea in China. Tidal current and waveare the dominant dynamic factors in Bohai Sea. With the development of the economyin the Bohai Rim, the research of dynamic factors in Bohai Sea has far-reachingsignificance for the development of ocean economy. In this paper, based on directwave and current measurements near Chengbei oil platform in Bohai Sea from asubsurface mooring with an Acoustic Wave and Current, characteristics of tidalcurrent and wave-current interaction are analyzed.Current spectra indicate that the semidiurnal (M2and S2) and diurnal (K1and O1)are the dominant constituents. Tidal Current Harmonic Analysis results demonstratethat the tidal currents of the principal semidiurnal rotate anticlockwise with depth.The main features of the variation of the four principal tidal constituents with depthdemonstrate that the currents in this region are influenced by the lower boundary layerand sea surface wind. Different vertical modes are calculated based on the EmpiricalOrthogonal Function (EOF) analysis of the Eastern component of the tidal currents,with a variance contribution for the zero-order mode of89.37%. The variancecontribution of the baroclinic model is minimal, which further reveals a strongbarotropic character for the Eastern component of tidal currents in this region. But theNorthern component indicates that it has strong baroclinicity.Statistical analysis of wave data indicates that the significant wave height ismainly less than3m, particularly around0.3m. The major peak direction is eastern,with a large fluctuation. When significant wave height is relatively large, the peakdirection is quite stable and the peak period is rather longer. Wave energy density ofthe frequency in the range from0.15Hz to0.3Hz is relatively large. When significantwave height is relatively large, wave energy density is large and the frequencydistribution is wide. Using data collected from AWAC, the effect of depth and current changes(particularly tidal) on waves and the effect of waves on tidal currents were examined.The possible interaction mechanisms between waves and tides are reviewed. Theseinclude bottom friction, depth, current refraction and modulation of the absolute andrelative wave period. The usefulness of tidal periodicity in identifying bothinteractions in wave parameters and the effects of the waves on the tide is noted. Forcorrect analysis, to obtain wave-free tidal conditions or tidally-averaged wavestatistics, it is particularly important to understand the interaction mechanisms. Forexample, the amplitude of the tidal current was found to be reduced in periods of highwaves.